1. Technical Field
The present invention relates to a technique for compression encoding a moving picture, and in particular to an image encoding device that compression encodes a plurality of moving pictures.
2. Background Art
Conventionally known standards for compression encoding (hereinafter simply referred to as encoding) used when transmitting a moving picture or recording a moving picture to a recording medium include MPEG (Moving Picture Experts Group) standards such as the MPEG 2 video standard (ISO/IEC 18818-2), the MPEG 4 visual standard (ISO/IEC 14496-2), and the MPEG 4 AVC standard (Moving Picture Experts Group phase 4 Advanced Video Coding, ISO 14496-10). Image encoding devices that conform to these standards are being developed.
One image encoding device that encodes a plurality of moving pictures in parallel is proposed in Japanese Patent Document 1. This image encoding device has a plurality of encoding processing units, each of which includes a frequency converter, a quantizer, and a variable length encoder. The image encoding device controls the output bitrate of each encoded moving pictures so as to maintain a constant overall bitrate in accordance with network transmission demands.
In this conventional image encoding device that encodes a plurality of moving pictures in parallel, an input moving picture is converted from a spatial domain to a frequency domain by a frequency converter, further quantized in accordance with quantization coefficients by a quantizer, and converted to variable length code and output by a variable length encoder. The image encoding device controls the output bitrate by performing quantization using quantization coefficients determined in accordance with a total value of the complexity of each of an input first moving picture and second moving picture.
Japanese Patent Document: Japanese Translation of PCT International Publication No. H09-512417
Since the aforementioned image encoding device that encodes a plurality of moving pictures in parallel has as many encoding units as the number of input moving pictures, it is suitable for situations where there is a constant number of input moving pictures.
However, an image encoding device is not necessarily used in a situation where the number of input moving pictures is always the same. For instance, a possible situation is one in which the image encoding device is part of a television broadcast receiver, and an arbitrary number of moving pictures that are selected by a user from among moving pictures broadcast on a plurality of channels are received in parallel to be subjected to encoding processing and stored in a compressed state to a recording medium such as an optical disc.
In order to deal with a situation where the number of input moving pictures is not necessarily always the same, the described conventional image encoding device is equipped with an equivalent number of encoding units to the maximum number of moving pictures permitted to be input. However, when the number of moving pictures selected by the user for input is less than the maximum number, some of the encoding units are unused and therefore redundant. This is undesirable in terms of effective usage of the internal circuits of the image encoding device.
The present invention was conceived in view of this problem, and has an object of providing an image encoding device that performs encoding processing in a manner that deals with an input of an arbitrary number of moving pictures and utilizes a limited number of encoding units effectively.